Carbon fiber-reinforced plastic (CFRP) is a lightweight material. The automotive industry has focused on producing a steel/CFRP hybrid part to reduce overall weight. After manufacturing, delamination can occur at the interface between the CFRP and steel owing to the hybrid part constituting dissimilar materials. However, most studies have focused only on designing the manufacturing processes for the hybrid part or evaluating the adhesive used at the interface. Therefore, it is necessary to predict the behavior of the interface after demolding the hybrid part. This study aimed to predict the interface behavior of a steel/CFRP hybrid part by considering its forming and cohesive properties. First, double cantilever beam (DCB) and end-notched flexure (ENF) tests were performed to obtain cohesive parameters, such as energy release rate of modes I and II (GI, GII). The experimentally obtained properties were applied to the bonding area of the hybrid part. Subsequently, a forming simulation was performed to obtain the stress of the steel blank in the hybrid part. The stress distribution after forming was utilized as the initial condition for spring-back simulation. Finally, the interface behavior of the hybrid part was predicted by a spring-back simulation. The simulation was conducted using the residual stress of steel outer and the cohesive properties on the interface, without the application of any external forces. The cases of spring-back simulation were divided as delamination occurrence and attached state. The simulation results for prediction of delamination occurrence and bonding showed good agreement in both cases with experimental ones. The proposed method would contribute to expanding the manufacturing of the hybrid part by stamping and reducing the manufacturing cost by prediction of delamination occurrence.

The spring-in phenomenon of the composite parts can affect the assembly process. This study aims to predict the spring-in phenomenon of a carbon fiber reinforced plastic (CFRP) part. Here, we predict the spring-in of the CFRP part using a coupled analysis of the forming and cooling processes during the stamping process. First, a simulation of the entire forming process, such as the transfer of the composite laminate, gravity analysis, and forming was performed to obtain the temperature distribution of the CFRP part. Subsequently, a finite-element (FE) simulation of the cooling process was conducted to predict the spring-in phenomenon of the shaped CFRP part using the temperature data obtained in the forming simulation. Finally, a CFRP part was manufactured and compared with the results of the FE simulation.

River processes and patterns are affected by changes in the watershed driven by natural and human‐induced causes. A sudden pattern alteration from a “white river” (bare soils) to a “green river” (vegetated) influences riverine biodiversity and can increase flood risk. Despite these significant impacts, knowledge on the triggers that kickstart feedback exacerbating changes in bio‐geomorphic patterns is insufficient. In this study, we collected and analyzed detailed monitoring data on a sandy, hydro‐morphologically active, and monsoon‐driven river in Korea. The surface area covered by vegetation has been increasing; this increase intensified after the 2014–2015 drought, which provided a window of opportunity for vegetation establishment. During the drought, pioneer vegetation densely colonized bare sandbars and temporarily exposed riverbed. Despite partial rejuvenation by several subsequent floods, succession to woody vegetation occurred, resulting in a stable vegetation cover. Narrowing and incision of a low‐water channel occurred, and secondary channels formed inside the floodplain. The results of this study show a rapid bio‐geomorphic alteration triggered by the shifts in flow regime in a river primed by human‐induced changes. Furthermore, modified monsoon‐driven rivers might be on the brink of similar bio‐physical alterations triggered through shifting flow regime following climate change, leading to increased flood risk and impacts on endemic biodiversity.

최근 친수성, 경관, 생태계 보전 등의 목적으로 자연 녹화 기능을 가진 다양한 친환경 호안 제품이 활용되고 있다. 호안을 포함하여 하천공사에 적용되는 자재들은 설계홍수시의 유수력에 대한 안정성이 보장되어야 하므로 이를 고려한 실험 기반의 안정성 평가가 필수적이다. 식생 호안의 경우 녹화 효과 외에도 식생 활착으로 인해 호안 표면이 보호되고 뿌리 발달로 인한 토양의 응집력과 내침식력 강화 효과가 있어 최근 그 활용이 증가하고 있다. 하지만 무식생 조건에서의 홍수 발생을 감안하면 무식생 조건에서의 허용 소류력 역시 중요하게 취급되어야 한다. 본 연구는 식생 매트형 돌망태 호안 재료를 대상으로 ASTM에서 제시된 시험법을 기반으로 동일한 시험체에 대해 식생 활착 여부에 따른 수리학적 안정성을 평가하였다. 실험 결과 시험체는 무식생, 식생 조건 모두 3회의 실험 유량 범위에 안정성을 보여주었으며, 토양 손실 역시 기준값 이하로 측정되었다. 식생 조건 실험의 경우 무식생보다 최대 1.4배의 소류력을 적용한 조건에서도 안정성을 유지하였다. 식생 시험체는 무식생에 비해 동일 유량에서 토양 유실이 적고 변형도 거의 발생하지 않았다. 본 연구의 결과는 식생 호안의 경우 그 효과를 극대화하기 위해서는 식생의 안정적인 활착을 고려하여 적절한 시공시기가 중요함을 시사한다. Various eco-friendly revetment products with natural greening functions have recently been used for amenity, landscape, and ecosystem preservation. Materials applied to river construction are required to ensure stability against design floods, so stability evaluations based on experiments are essential. The use of vegetation revetment is increasing because, in addition to the greening effect, the bank surface is protected by the vegetation establishment and the cohesiveness and erosion resistance of the soil due to root development. On the other hand, the allowable shear stress in non-vegetated conditions should also be considered important, considering floods before vegetation establishment. In this study, the hydraulic stability of the vegetation mat-type gabion revetment material was evaluated based on the ASTM test method. The specimen showed stability in the three experimental discharge conditions in both non-vegetated and vegetated conditions, and soil loss was below the reference value. Under vegetated conditions, stability was maintained even when an up to 1.4-fold flow discharge was applied. Soil loss and deformation were less than in the non-vegetated cases. These results suggest that considering the vegetation establishment, proper construction time is important to maximize the effect of vegetation revetment.

In this study the lateral migration of an alluvial river, which occurred between 2015 and 2021 at the Gopyeong site of the Naeseong Stream was quantitatively analyzed and the relationship between the hydraulic characteristics of the floods and bank erosion was examined. Bank erosion began in the upstream part of the study reach and then was concentrated on the downstream part beyond the bend apex, showing lateral and downstream migration. Average annual migration rate is 5.6 m/yr. Annual change of the crosssection shows that the lateral migration is accompanied by the retreat of the outer bank, formation of a pointbar at the inner bank together with the incision of the low water channel bed that appeared throughout the river. Volumetric sediment relocation brought forth by these processes was evaluated. Bank erosion is controlled mainly with floods, and eroded area is proportional to the duration of inundation. The results of this study imply that a series of drone/aerial images are useful for the quantitative analysis on the lateral migration of alluvial rivers.

Over the last decade, rapid vegetation colonization and changes in channel morphology have been observed in the Naeseongcheon Stream in South Korea, which were linked to short-term hydrological fluctuations under a changing monsoon climate. The surface area covered by vegetation has been increasing; this increase intensified after the 2014–2015 drought, which provided a window of opportunity for vegetation establishment. During the drought, pioneer herbaceous vegetation densely colonized the lower floodplains, including bare sandbars and temporarily exposed riverbed. Although the colonized lower floodplain and river banks were partially rejuvenated by several subsequent floods, succession to woody vegetation continued, resulting in stable vegetation cover in areas that had previously been bare. Moreover, sediment carried by flood water was deposited on and around the vegetated areas, and the low-water channel was incised, causing vertical development of river topography. In addition, the main channel width decreased in previously relatively wide sites, and secondary channels formed. The results of this study show that river rejuvenation by floods may decrease owing to systemic changes in the river system. Therefore, we concluded that the Naeseongcheon watershed was primed by human-induced changes, which made the river system more susceptible to changes in rainfall and discharge due to climate change. Furthermore, after the initial vegetation colonization, changes in nutrients and temperature created a positive feedback loop, which reinforced vegetation establishment.

Riparian vegetation patches growing on river banks and floodplains influence in‐channel and overbank hydromorphological processes. The current knowledge on patch‐scale hydrodynamics is largely based on laboratory flume experiments with simplified vegetation. The aim of this study is to provide new understanding of the flow and wake characteristics for real riparian vegetation patches based on field‐scale experiments with natural willows, in order to inform hydromorphological and ecological modelling. The focus was placed on the effects of foliage as the main driver of the seasonal changes in vegetation and on the influence of the flexibility‐induced reconfiguration on the flow in the wake and around the patches. The patch drag, defined by its flow blockage factor, was increased by 3.0–4.4 times by the presence of foliage and decreased by up to 60% because of the streamlining and reconfiguration of foliage with increasing flow velocity. Such large changes in the patch drag altered the flow and wake characteristics, affecting the onset of a patch‐scale vortex street. Seasonality and flexibility modified the patch sheltering effect, that is, the magnitude of velocity, turbulent kinetic energy, and bed shear stress reduction in the wake, relative to the background level. In the presence of foliage, mean flow velocity and bed shear stress in the wake were reduced on average by ~50% and ~70%, respectively. The sheltering effect was lower for the leafless conditions than for the foliated conditions. For the foliated cases, the spatial extents of the over‐depth and the near‐bed sheltered region were on average 1.5 and 1.8 times larger than in the corresponding leafless cases, respectively. Overall, seasonal changes in vegetation and flexibility‐induced mechanisms were identified as key controls for the flow associated with patches of riparian vegetation, with major implications on developing models for predicting hydromorphological processes and the potential to preserve and create habitats.

Multi-materials of metal-polymer and metal-composite hybrid structures (MMHSs) are highly demanded in several fields including land, air and sea transportation, infrastructure construction, and healthcare. The adoption of MMHSs in transportation industries represents a pivotal opportunity to reduce the product’s weight without compromising structural performance. This enables a dramatic reduction in fuel consumption for vehicles driven by internal combustion engines as well as an increase in fuel efficiency for electric vehicles. The main challenge for manufacturing MMHSs lies in the lack of robust joining solutions. Conventional joining processes, e.g., mechanical fastening and adhesive bonding involve several issues. Several emerging technologies have been developed for MMHSs’ manufacturing. Different from recently published review articles where the focus is only on specific categories of joining processes, this review is aimed at providing a broader and systematic view of the emerging opportunities for hybrid thin-walled structure manufacturing. The present review paper discusses the main limitations of conventional joining processes and describes the joining mechanisms, the main differences, advantages, and limitations of new joining processes. Three reference clusters were identified: fast mechanical joining processes, thermomechanical interlocking processes, and thermomechanical joining processes. This new classification is aimed at providing a compass to better orient within the broad horizon of new joining processes for MMHSs with an outlook for future trends.

It is very important to secure sufficient river maintenance flow for the ecosystem, since the ecosystem in the downstream section of the dam is greatly affected by the stream maintenance flow from the dam. However, the amount of discharge from the Seomjingang Dam is decreasing year by year, this study estimated the ecological flow required for the downstream section of the Seomjingang Dam, which is known as the habitat of the endangered Acheilognathus somjinensis, in order to secure the river flow of the Seomjingang Dam. For this purpose, the proper discharge was calculated using the PHABSIM model, which is a hydrological survey and physical habitat simulation method, and the proper discharge of other fish species were also comprehensively reviewed. As a result of this study, the current river maintenance flow at the Seomjingang Dam partially satisfies the ecological maintenance flow including the Acheilognathus somjinensis in the downstream section of the Seomjingang Dam. However, this is recognized as the minimum discharge to maintain the ecology in the downstream section of the Seomjingang Dam, and it would be more desirable to secure larger river maintenance flow than this. This study can contribute the determination of the river maintenance flow of the Seomjingang Dam by proposing the river maintenance flow considering the fish habitat environment in the river.

INTRODUCTION:The aim of this study was to investigate the influence of various apical preparation designs for surgical endodontics on stress concentrations in the mesial root of the mandibular molar under different experimental conditions using finite element analysis.METHODS:We designed 2 apical preparation groups according to whether an isthmus was present or not. Each group contained 4 subgroups according to the size of the apical preparation. We constrained the displacement of all nodes at the base of the supporting bone and applied a force of 150 N to the vertical axis. We analyzed stress generation and concentrations numerically for the groups and subgroups.RESULTS:In the subgroups, the von Mises and maximum principal stresses reduced gradually according to the enlargement of the prepared cavity. However, when the preparation extended excessively in the isthmus preparation groups, the situation reversed (ie, both von Mises and maximum principal stresses increased).CONCLUSIONS:Within the limitations of this study, the apical preparation design influenced the distribution of stress concentration. Unlike the overall pattern in which stress decreased as the amount of apical preparation increased, stress increased when the amount of residual dentin was extremely thin.

Prepreg compression molding (PCM) is a well-known process for manufacturing of carbon fiber reinforced thermo-plastics (CFRTP) products with high quality and production rate. However, the design method used for the development of automotive parts has not been clearly presented. In this paper, we propose a process chain that can satisfy the stiffness of existing steel products. First, the CFRTP product of a B-pillar reinforcement to satisfy the bending deformation of an existing product is designed using a structural analysis and genetic algorithms. Next, forming conditions of the product are determined by a forming analysis. To investigate the feasibility regarding the mass production of the PCM process, a rapid heating and cooling system was applied to PCM molds. The heating and cooling times of the molds were calculated using a computational fluid dynamics analysis. Finally, a CFRTP product was fabricated and its bending deformation, dimensional accuracy, and weight were evaluated.

This study compared the maximum screw-in forces of various instruments during their movements. Forty simulated canals in resin blocks were randomly divided into four groups (n = 10): ProTaper Universal F2, ProTaper Gold F2, WaveOne Primary, and WaveOne Gold Primary. To standardize a lumen size, all artificial canals were prepared with ProTaper Universal F1. The rotation speed was set at 350 rpm with an automated 4 mm pecking motion at a speed of 1 mm/s. The pecking depth was increased by 1 mm for each pecking motion until the file reached the working length. During instrumentation, screw-in forces were automatically recorded by customized software. Maximum screw-in forces were analyzed by one-way ANOVA and Tukey’s post hoc comparison with the significance level at 0.05. WaveOne Gold files generated the lowest maximum screw-in forces, followed by ProTaper Gold, WaveOne, and ProTaper Universal (p < 0.05). Under the condition of this study, heat-treated nickel–titanium (NiTi) files with smaller cross-sectional area, fewer contact points, and reciprocating movements resulted in a lower screw-in effect.

Flow hydrodynamics and transport processes are expected to be highly complex on floodplains, riverbanks and channel bars growing distinct patches of shrubs and trees. Current understanding on patch-scale hydrodynamics is largely based on flume experiments with simplified vegetation of a limited physical scale. This paper reports preliminary results on the lateral and wake flow characteristics of stream-scale willow patches having dimensions of meters. We investigated emergent patches of Salix subfragilis in an experimental channel with a water surface width of ~6 m and water depth of ~1 m. The experiments covered both leafless and foliated conditions at the two ambient mean velocities of 0.3 and 0.5 m/s. The flow field was measured with an array of nine Acoustic Doppler Velocimeters. The flow deflection around the patch was stronger under the foliated compared to the leafless conditions. The greatest velocity deficit downstream of the patch was recorded under foliated condition at the lower mean flow velocity. At the higher mean velocity, the depth-averaged turbulence intensity within the patch was higher for the foliated condition while the opposite was observed for the lower ambient velocity. Generally, the depth-averaged turbulent kinetic energy and turbulence intensity showed large variability within the patches. The wake flows were found to extend up to several tens of meters downstream from the patches, indicating that real-scale riparian patch mosaics are characterized by highly complex flow fields. In the future, the data will be used to develop the numerical modeling of shrub-vegetated flows at real scale.

Feedback between turbulence, sediment transport and morphology is important for natural stream managements. While experimental studies have focused on the mean flow and turbulence with mimic vegetation such as cylinders and bamboo sticks, this study presents preliminary results of mean flow, turbulence and morphological changes in the large–scale outdoor channel with real willow patches, consisting of foliated and leafless vegetation. The mean flow showed the steady wake regions and the velocity gradient near the interface between the vegetation patch and free stream. The large momentum exchange occurred at the shear layer where the Reynolds stress was elevated and it was consistent with enhanced regions of sediment deposition downstream of the patches. These data will be very help to further understand landform process in vegetated channels.

This study investigates possible causes for accelerated vegetation recruitment and growth in an unregulated sandy stream in Korea. Flow and sediment regime, represented here by critical bed shear stress, is considered a dominant physical factor affecting the stability of sediment bars with vegetation at germination and seedling periods. A good inverse correlation is obtained between the area of vegetation expansion on sediment bars and the annual peak flow during early summer (June and July) where other minor effects seem not to be important. Three comparative reaches are selected in a stream; one strongly meandering reach, one moderate, and one mildly meandering reach. Hydraulic calculations are made for the whole stream reaches using a verified numerical model to evaluate two-dimensional distribution of the critical bed shear stresses at those reaches. Results are compared with past aerial photos of the study stream. Other critical physical factor of soil moisture is considered not to be limiting to the present case of sandy stream. The results are relatively in good agreement between the calculated distribution of bed shear stress and actual distribution of vegetation on the riparian sediment bars, indicating that stability of riparian sediment bars would be critical for vegetation recruitment and growth.

The hole-clinching process is one of the mechanical methods for joining dissimilar materials, such as aluminum alloy with advanced high-strength steel, hot-pressed steel, and carbon fiber reinforced plastics, employing forming technology-based methods. In joint design, the analysis of the failure-mode dependent joint strength is a crucial step in achieving structural performance for practical applications. In this study, the influence of the geometrical interlocking parameters on the failure-mode dependent joint strength was investigated in order to design the geometrical interlocking shape of the hole-clinched joint to achieve a target joint strength. Moreover, the failure process of the hole-clinched joint under pullout loading condition was studied to determine the geometrical interlocking parameters that affect joint strength. Based on the results of the finite element analysis, an analytical approach for the failure-mode dependent joint strength was proposed to predict the strength of the hole-clinched joint. In addition, the proposed analytical approach was applied to the hole-clinching process with dissimilar materials. Its effectiveness was then verified using the cross-tension test. Accordingly, it was found that it was possible to predict the failure modes and joint strength with a maximum error of 7.8%.